Indian Ocean

Indian Ocean, the smallest of the Earth’s three great oceans, located mainly in the Southern Hemisphere, and bounded on the west by Africa, on the north by Asia, on the east by Australia and the Australasian islands, and on the south by Antarctica. No natural boundary separates the Indian Ocean from the Atlantic Ocean, but a line about 4,020 km (2,500 mi) long on the meridian 20° east, connecting Cape Agulhas at the southern end of Africa with Antarctica, is generally considered to be the boundary.

The total area of the Indian Ocean is about 73.4 million sq km (28.3 million sq mi). The ocean narrows towards the north, and is divided by the Indian subcontinent into the Bay of Bengal on the east and the Arabian Sea on the west. The Arabian Sea sends two arms northwards—the Persian Gulf and the Red Sea. The average depth of the Indian Ocean is about 4,210 m (13,800 ft), or slightly greater than that of the Atlantic, and the deepest known point is about 7,725 m (25,344 ft), off the southern coast of the Indonesian island of Java. In general, the greatest depths are in the north-eastern sector of the ocean, where about 130,000 sq km (50,000 sq mi) of the ocean floor lie at a depth of more than 5,486 m (18,000 ft).

The Indian Ocean contains numerous islands, the largest of which are Madagascar and Sri Lanka. Smaller islands include the Maldive group and Mauritius. From Africa the ocean receives the waters of the Limpopo and Zambezi rivers, and from Asia those of the Irrawaddy, Brahmaputra, Ganges, Indus, and Shatt Al Arab rivers.

As a rule, the winds over the Indian Ocean are gentle, with frequent extended periods of calm. Tropical storms occur occasionally, however, particularly near Mauritius, and the ocean is notable for seasonal winds called monsoons. It was the shifting of the Indian and Burmese tectonic plates that caused the undersea earthquake of December 2004 that measured 9.1 on the Richter scale. The massive tsunami, with walls of water approaching 15 m (50 ft) in height, which followed killed an estimated 150,000 coastal dwellers all around the Indian Ocean ring from the eastern African coast in the west to Malaysia in the east.